Dynamo Regulator Charger Circuit for full-time lights...



loquin

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Jan 11, 2008
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Well, I've been doing some digging over at the texas instrument semiconductor site, augi. They have a single-chip SLA (sealed lead acid) charger integrated circuit that would work in place of the complicated circuitry at the link above, and the electronics part count would drop to about 11 parts. About 6 small resisters, a couple of capacitors, an inductor, a transistor, and the IC. The whole circuit could fit on a pc board about 1.5 inches by 3 inches...
 

bennyboy

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Mar 9, 2008
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would you mind posting the required parts I would be interested in building this myself really what that is doing is giving you a constant a/c current you get that up to a constant 12v a/c and you might as well just slap a radio and a cigarrette lighter on your bike so you can charge your cell phone as you drive around. Im sure those generators are so smooth that being motorized would be more than capable to run a full 12 volt system that would be wonderful.
 

loquin

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I haven't done the design for a 6V unit yet. But, the SLA charger IC has three different charging modes you can configure. Plus bells & whistles (LED feedback, for instance) if you wanted to include it. The basic configuration uses an external transistor to pass the DC power to the battery, a bridge rectifier & capacitor for the AC-DC conversion, three small resistors in the feedback circuitry, a choke and and a blocking diode. The IC monitors the battery voltage/internal resistance for an initial fast charge and then a trickle charge when the fast charge is done. Thus, no damage to the battery due to overcharging.

In the next couple of weeks, I'll go through the design process and post a circuit schematic & parts list.

The real issue is that the bicycle dynamos are low power. Only 3 watts. (Now, they WILL put out up to 6 watts at higher speeds, but, you should only count on 3 watts.) In addition, when the bike stops, the hub (or wheel driven) dynamo's output also stops. Using a transformer or voltage doubler to achieve 12 volts will not increase the amount of power they can deliver - it is still limited to 3 watts.

Because of this, the ideal configuration for these devices would be to have them charge a small battery - one which could be used to provide power to a 3 W light for an hour or two on its own. While driving the bike during the day, all the power could be used to recharge the battery. At night, any power not used to drive the lights could also be used to maintain charge. It appears that the TI SLA battery charger IC would fit the bill perfectly for our needs.

I've located a small (4 x 2.5 x 7/8 inch) 6V, 1.2 amp-hour sealed lead-acid battery, available from multiple sources. It would provide 6V, 3W for about 2.5 hours. As I mentioned in another thread, I believe you could modify a 3 W LED 2 or 3 Cell Mag-lite to be a very nice headlight. (Even IF you drew slightly more than 3 watts from the battery, there should be enough excess capacity in a normal driving routine to maintain a charged battery.)

I would like to design, then build a lighting and battery charging circuit, using the Sturmey-Archer X-FDD Front Brake/Dynamo hub (which I ordered over the weekend). I'll eventually do this, and document the project here.

The problem I'm having on the home front is that we're trying to get our house ready to go on the market for a possible move... So, most of my spare time is taken up with that for a while. So, I can't jump on this thing the way I'd really like to...:-|
 
B

BSA

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Apparantly on Sheldon Browns website he just shoved the dynamo's output through a bridge diode and strait into a lead acid battery.

BSA
 

loquin

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Apparantly on Sheldon Browns website he just shoved the dynamo's output through a bridge diode and strait into a lead acid battery.

BSA
Yes - you can do that. And, it will work OK... for a while. The battery itself will act as a regulator to a certain extent, as it will limit the output voltage to the maximum cell voltage. However, the dynamo current will continue to feed into the battery, even after it is fully charged, and this will lead to early battery failure.
 
B

BSA

Guest
Yes - you can do that. And, it will work OK... for a while. The battery itself will act as a regulator to a certain extent, as it will limit the output voltage to the maximum cell voltage. However, the dynamo current will continue to feed into the battery, even after it is fully charged, and this will lead to early battery failure.
I never thought of that. I guess that sturmey archer x-fdd kills two birds with one stone, good braking and a good power source. i'm staying tuned to this project.

BSA
 

Nerobro

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Mar 20, 2008
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And if you really are kinky, you can spend $9 on a bridge rectifier and a 12v regulator. Problem solved ;-)
 
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